1. The problem statement, all variables and given/known data This question has two parts. There is a quarter or radius R that is charged with a net force of Q. A point like charge of net charge q,is at a distance z from the center of the quarter. Q1: Under what condition could we use Coulomb's law to find the magnitude the force between the quarter and the charge. A1: My answer is when the charge on the Quarter is concentrated at its center. Q2: In an experiment the force was found to be given by , F= Qq/A2ε°(1 -( z/(z^2+R^2)^2/2). Where A is the area of the quarter. Apply your condition from Q1 to show this equation is consistent with Coulomb/s law. sorry it looks like a mess. 2. Relevant equations none 3. The attempt at a solution I tried to find the limit as R approaches zero. the part in the first set of brackets becomes zero, then so does the whole expression, so I was wondering if I approached this completely wrong, or if it's a matter of properly rearranging the expression. Thank you in advance.